Production methods for aqueous emulsion, fine powder and stretched porous body of modified polytetrafluoroethylene

A production method for an aqueous emulsion of modified polytetrafluoroethylene, which is a method to obtain an aqueous emulsion of non-melt-moldable modified polytetrafluoroethylene particles having an average primary particle diameter of from 0.10 to 0.30 μm, by subjecting tetrafluoroethylene and a perfluoroalkyl ethylene represented by the following formula (1) to emulsion polymerization in an aqueous medium, in a polymerization reactor using a polymerization initiator, in the presence of a fluorinated anionic surfactant having a LogPOW of from 2.4 to 3.4,

• wherein
• an amount of the perfluoroalkyl ethylene to be used, is from 120 to 3,000 ppm (by mass) to the final production amount of the modified polytetrafluoroethylene,
• the entire amount of the perfluoroalkyl ethylene is charged to the polymerizarion reactor such that at the initiation of the emulsion polymerization, the entire amount of the perfluoroalkyl ethylene is present,
• an amount of the fluorinated anionic surfactant present in the emulsion polymerization is from 1.09 to 2 mass % based on the final production amount of the modified polytetrafluoroethylene,
• and
• as the polymerization initiator, either one or both of a combination of a bromate and a bisulfite or sulfite, and a combination of a permanganate and oxalic acid, are used:
• CH2═CH—Rf (1)
• wherein Rf is a C1-6 perfluoroalkyl group.